Nanoscale optical microscopy in the vectorial focusing regime

It has been known since 1959 that the focal-plane intensity distribution produced by focusing polarized light with a high-numerical-aperture lens should be highly asymmetric. Remarkably, the consequences of this fundamental effect in direct image acquisition have remained unexploited, although vectorial effects have been observed in the contexts of free-space focusing, molecular fluorescence and photolithography. By using extreme-numerical-aperture (values of 3.5), solid-immersion microscopy we have obtained images of a silicon integrated circuit showing, for the first time, the dramatic influence of polarization on their spatial resolution, with values from 100nm to 250nm. Our data show that polarization-sensitive imaging can substantially surpass the scalar diffraction limit embodied by classical formulae such as Sparrow's criterion. Such performance will have an impact on activities such as integrated-circuit failure analysis, where optical inspection faces serious challenges from the sub-100-nm feature sizes routinely used in production devices. © 2008 Nature Publishing Group.